Film drive starting apparatus



Feb. 25, 1941- M. E. COLLINS FILM DRIVE STARTING APPARATUS Filed April23, 1938 gin um": km

2 m D k k .w/ w w -W l w W M. 5 m 12 m m Hm\ 0 u 7 4 w a; I 4 m E g w x\n W? v IA j 111*! m a fur fi v 7 u 1 1 7 [Kata/e 0 COLL/NS AttorneyPatented Feb. 25, 1941 I UNITED STATES azsam rum DRIVE sTAnTmG ArrAnATusMilford E. Collins, Hollywood, Calif., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application April 23, 1938, SerialNo. 203,880

9 Claims.

This invention relates to sound film apparatus, and particularly to afilm drive starting system whereby the iilm advancing elements areaccelerated to their uniform running speed in a shorter period of timethan heretofore.

It is well known in the art of film recording and reproduction of soundthat thefilm should be advanced or driven past a modulated light beam inthe case of recording, and past a constant intensity light beam in thecase of reproduction, at a constant uniform speed. This is essential forthe maintenance of high quality sound reproduction.

, A preferred method of maintaining constant film speed at thetranslation point,'as the point of contact between'the film and lightbeam is usually called, is to pass the film at this point over a drum orsmooth roller interposed between feed and takeup sprockets. Ordinarilythe film drum has a mass attached thereto in the form of a flywheel andmay be rotated solely by the pull of the film passing thereover,although preferably the drum is positively driven through a flexible.connection such as is obtainable by a magnetic clutch. For anillustration of such a magnetic clutch, reference is made to the E. W.Kellogg Reissue Patent 19,270, of August 14, 1934.

In the usual sound recorder or reproducer; the

film is threaded through the machine from the supply reel to a takeupreel. A starting switch is then thrown to energize the driving motor toaccelerate the apparatus and bring the film up to a uniform speed, whichis usually 90 feet per minute. If all elements were positively driventhrough mechanical connections, the period between the time the switchis thrown and the time uniform constant, speed is obtained would dependupon the power of the motor. As arule, the period of time for the motorto obtain constant speed is a few seconds after the switch is thrown.However, as the flywheel and drum combination has considerable inertiaand is not positively connected to the driving motor except through onlysufiicient magnetic coupling to maintain its speed during operation, theperiod required to bring the drlmi up to speed is considerably longer.Furthermore, there is a likelihood of film damage due to slipping ofthefilm over the drum as well as the wastage of film during the long periodof starting.

. The present invention, therefore, has for its primary object theshortening of the starting time of fllm recording and reproducingapparatus. j Another. object of the invention is to automatic; callyincrease the stiffness of the flexible connection between the film drumelement and the driving element during the starting period.

A further object of the invention is to auto- I matically increase themagnetic coupling .of a magnetic clutch between the driving portion of 5the apparatus and the flywheel and drum elements and to automaticallyreduce the magnetic coupling to operative conditions at a predeterminedsubsequent time such as when the apparatus has attained uniform speed.

Although-the novel features which are believed to be characteristic ofthis invention are pointed out with particularity in the claims appendedhereto, the manner of its organization and the mode of its operationwill be better understood by referring to the following description readin I conjunction with the accompanying drawing forming a part thereof,in which the single figure diagrammatically represents the essentialfilm drive elements suchas the drum, flywheel and magnetic clutch of arecorder or 'rep'roducer, and a schematic wiring diagram of theapparatus embodying the invention.

Referring now to the drawing, a. motor 5- through a gear reduction box 6drives a main 25 gear 3, which meshes with an intermediate gear 8 fordriving a gear 8. The gear 3 is adapted to rotate upon a bearing formedby a stationary sleeve or quill ii located within'an extension H of awall 82 of a recorder or reproducer. The

drive shaft l4 driving the gear I also directly drives a feed or drivesprocket 15. Upon a 1'0- tatable shaft I! is mounted a smooth drum itover which the film passes at the time the light beam strikes it. Uponthe other end of the shaft ii is mounted a flywheel 2|! having a coppercylindrical member 2i inserted in one side thereof. The gear 9 drives amagnetic coil 25 mounted upon an enlarged hub portion 26, the 001116magnetizing a serrated cup member 25' formed 4 integral with hub 26,thus producing a magnetic fleld between pole pieces 21 and 26 in whichthe member it rotates. Electrical current is supplied to the coil 25through slip rings 30 and Si and connections 32 and 33, respectively. 45

The above-described apparatus may be employed ineither a recorderwherein the modulated light beam is projected on a sensitized film whilepassing over the roller ill, or may be a portion of a reproducer whereina constant intensity 50 .light beam is projected through tli'e'processedsound track portion'of the film overhanging the roller to modulate thebeam before impression upon a photosensitive pickup element such as aphotocell. It will be realized, of course, that the motor being directlyconnected to the sprocket "l5 and other sprockets (not shown) of theapparatus, these sprockets and, consequently, the film, will be broughtup to speed as rapidly as the motor accelerates. However, since theroller l8 is connected to the driving apparatus only through thecoupling produced by the magnetic.

field existing between pole pieces 21 and 28, there will be slippage ofthe film over the roller in accordance with the rate of acceleration andthe strength of the field. Even though this slippage may not besuflicient to damage the film, it nevertheless increases the period ofstarting of the recorder or reproducer. r

f The present invention, therefore, contemplates shaking the connectionbetween the positively driven element or magnet 28 and flywheel androller combination l828 more positive by increasing the strength of themagnetic field during the acceleration period, after which the magneticcoupling may be reduced to a value which has been found suitable toprovide the proper 'the apparatus. Direct current is supplied to thewinding 25 from a direct current energy source 4| under control of aswitch 45 over a pair of conductors 40. J Ordinarily and duringoperating conditions, the energy is supplied-over conductor 42 andthrough .a series resistance 43 and a meter. 44. However, to increasethe coupling between driven and driving elements of themagnetic clutchduring starting, the current in the winding 25 is increased by shortingout the resistance 43 and meter 44 by an automatic thermal controlledrelay combination. This short circuit is formed as follows: When theswitch 38 is thrown to energize the motor 5, a two-pole, normally open,220-volt relay 48 is also energized,

' completing a circuit from point 48 over conductor 48, through theright hand contact element 5|| of relay 5|, over the right hand contactelement 53 of relay 48, over conductor 54 to the point 55.

Closure of the relay 46 also completes a circuit from the battery 4|,over conductor 42, over conductor 58, through a hot-wire resistanceelement 58, conductor 80, the left hand contact member 8| of relay 48,conductor-82, the left hand element 83 of relay 5|, and the right handelement 58 of relay 5|, conductor 48 and back to the battery 4 throughpoint 48. This circuit heats and thereby lengthens the hot-wire element58 allowing a contact member 85, which is heldv under tension by wire58, to move to the right and make contact at 88 with member 81. Whencontact is made at 88, the relay 5| is energized 'over a circuit frombattery 4|, over conductor 42, winding of relay 5|, conductor 88.element 81,

element 85, conductor 10, the right hand element 58 of relay 5|,conductor 48 to battery 4| through point 48. Thus, contact at 86 causingoperation of relay 5| not only breaks the-circuit just traced,

but also the short-circuit across resistance-43 meter 44. Removal oftheshort circuit decreases the..'current to coil." and reduces the removingthe short 'circ1iit from"said impedance magnetic coupling to operatingconditions. To

1 maintain the relay5| energized after operation,

element 83 makes contact at 12 to complete a new energizing circuit frombattery 4|, over conductor 42, through winding of relay 5|, over con- 5ductor 13, the left hand contact element 83 of relay 5|, the right handelement 53 of relay 48, conductor 54, resistance 43jmeter, 4'4 and backto battery 4|. The break .between contact 15 and element 83 removes theheating circuit for the 10 hot-wire 58 which permits the contraction ofthe wire 58 to resetthe tension element 65.

In the operation of this circuit various predetermined times ofoperation are obtainable by adjustment of the tension in the element 8515 which varies the distance between the contacting elements 85 and 81,the length of time required to cause contact at 88 determining thelength of time the short-circuit exists across elements 43 and 44.

In the operation of the above starting apparatus, switch 45 is firstclosed to permit adjustment of rheostat 43 to provide the properoperating current to coil 25 as indicated by meter 44. It is then onlynecessary to close the'switch 38, which 25 simultaneously energizes thedriving motor 5 and the master relay 48. Immediately the full voltage ofthe source 4 is impressed on the winding 25 to produce a strong magneticfield and bring the flywheel mass 28 and roller |8 up to speed practi-30 cally as rapidly as the directly driven elements; of the apparatus.At the same time the current is fed through the hot wire 58 which beginsto lengthen and in accordance with "its setting should make contact at86 at the time the ap- 5 paratushas reached uniform speed, thus reducingthe current to the coil 25 and permitting the apparatus to normallyfunction.

It has been found that the starting speeds have been materially,shortened with the above-de- 0 scribed system to accomplish a saving-offilm and time in film recording and a saving of film leader and time insound reproduction.

Iclaimz, a

1. Apparatus for decreasing the starting time 45 of film drive apparatuscomprising a motor, film advancing sprockets directly connected to saidmotor, film advancing elements magnetically connected to said motor, andmeans for strengthening the magnetic connection during the period 50 ofacceleration of said motor.

2. Apparatus for decreasing the time of acceleration of film drivingelements comprising a driving motor, a plurality of sprockets directlyconnected to said motor for advancing film 55 through said apparatus,another film advancing element,'a magnetic clutch interconnecting saidlast-mentioned film advancing element and said motor, and means forincreasing the magnetic field of said' magnetic clutch duringacceleration 60 of said apparatus and for decreasing said magnetic fielda predetermined time after starting.

3. Apparatus for decreasing the time of acceleration of a film drivingmechanism comprising 65 a magnetic coupler and circuit control apparatustherefor comprising a plurality of magnetic relays and a thermal relay,means for energizing one of said magnetic relays, a plurality ofimpedance elements short'circllited by operation of said re-' lay,operation of saidrelay also energizing said v thermal relay, and meansfor; operating another of said plurality of relays by operation of saidthermal relay. the operation of said second relay elements whilemaintaining energization of said second. relay.

4. Apparatus for controlling the acceleration necting said filmadvancing means to said mag 1 netic device, a plurality of impedanceelements in the energizing circuit between. said second source of energyand said magnetic device, a magnetic relay adapted to short-circuit saidimpedance elements upon operation thereof,. a

second magnetic relay adapted to remove said short circuit, and timedelay means energized by operation of said first relay .ior energizingsaid second relay.

5. Apparatus for decreasing the starting period of film drive apparatuscomprising a driving motor, field producing means, a plurality of filmadvancing elements directly connected to said motor, another filmadvancing element having mass,

said last-mentioned element being connected to said driving motorthrough the reaction of the field-of said field producing means, asource of energy for said field producing means, a circuit connectingsaid source and said fieldproducing means, a plurality of impedanceelements in said circuit, and means operable upon energization of saidmotor for short-circuiting said impedance elements only during theperiod of acceleration of said motor.

6. Apparatus inaccordance with claim 5 in which said last-mentionedmeans comprises a thermal time delay relay adapted to remove theshort-circuit from said impedance elements a predetermined time after,energization of said motor.

'7. A film drive starting system comprising a 'motor, a magnetic fieldproducing element, a plurality of film advancing elements directlydriven by said motor together with said magnetic field producingelement, a rotatable element located in said magnetic field, and meansfor increasing the energy supplied to said field producing elementduring a predetermined periodof rotation thereof.

8.'Apparatus for decreasing the starting time of a rotating elementcomprising a motor, magnetic means for coupling said motor to saidrotating element, a source of energy, and means independent of saidrotating element and said motor for supplying a definite amount ofenergy from said source to said magnetic coupling during theacceleration period of said motor, and another definite but lesseramount of energy after said motor has reached a uniform speed.

9. Apparatus in accordance with claims in which said energy supply meansincludes a hot wire relay.

MILFORD 'E. COLLINS.

